> as a gateway probe. The latter is basically a traceroute packet to> sunsite.unc.edu or tsx-12.mit.edu, with a TTL of 2 (this usually elicts> an ICMP redirect and/or a time exceeded, from which we can piece together> the gateway's IP).

The gateway probe is tricky. You may start routing through one of the millionsof machines erroneously shipped by vendors with routing enabled or via thewrong router. There is a router discovery protocol. Its less supported but a lot safer. Listening for OSPF/RIP/RIP2 can also do the detection sometimes.

Its probably not that big an issue but if you install a network of machinesthat accidentally all choose to route via the tiny isdn router on the edgeof the lan not via the main router bad things occur.

At the minimum you need to verify that the icmp time exceeded comes from ahost which you cannot directly reach. If you can directly reach the 2nd or3rd hop that errors then you have found a secondary host misconfigured asrouter, or a secondary router, and it just told you the correct router touse. Sometimes you'll get a redirect, sometimes you dont.

If its an older 3com office connect firmware you actually start crashing the3com box even ;)

Alan

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